DE102022106063A1 - Method for monitoring the operation of a pump, preferably a centrifugal pump - Google Patents

Abstract

The invention relates to a method for monitoring the operation of a pump, preferably a centrifugal pump (1), with a multi-phase, in particular three-phase drive motor, with the method steps: - Determining whether the pump is working in a stable operating state, - If a stable operating state is present, Monitoring at least one characteristic variable of the drive motor to determine whether an impeller blockage is present, - if an impeller blockage is detected, activate a freewheel of the pump impeller, - otherwise, evaluate the frequency spectrum of the motor current to detect an impairment of the pump and switch off the motor by running down a decreasing speed ramp, if an impairment of the pump is detected.

Description

The invention relates to a method for monitoring the operation of a pump, preferably a centrifugal pump, with a multi-phase, in particular three-phase, drive motor.

Sewage pumps, also known as dirty water pumps, enable the pumping of grossly contaminated water, which often contains solid components of various organic, inorganic or mineral origins. Sewage pumps are preferably built in one stage and are generally not self-priming. The use of the impeller shapes depends on the fluid being pumped. Channel wheels are often used as impellers, especially in the form of a one-, two- or three-channel wheel, each closed or open. However, there are also designs with open single-channel and diagonal impellers as well as free-flow impellers.

The solids carried in the fluid can cause deposits to adhere to the impeller structure, which can lead to an impairment of the pump function and an associated impairment of the pump efficiency. In the worst case scenario, the impeller is completely blocked, meaning that further rotation is no longer possible. If the drive is not switched off in such a case, mechanical damage to the pump hydraulics or an overload of the electric drive motor may occur. Against this background, it is important that the pumps, which often operate independently over a long period of time, are continuously monitored and are automatically deactivated in the event of an emergency.

However, since the emergency shutdown means a significant intervention in the pump operation, it is desirable to be able to differentiate between acute and less acute fault cases and to be able to take suitable, individual countermeasures in each case. Especially when the impeller is dirty, the pump can continue to work, but the efficiency that can be achieved is impaired, which worsens the energy balance.

Measures are therefore being sought to be able to differentiate between error cases during pump operation and initiate error-dependent countermeasures.

This task is solved by a method according to the features of claim 1. Advantageous embodiments of the method are the subject of the dependent claims. In addition, the task is also achieved by a pump, in particular a centrifugal pump, with a pump control according to the features of claim 14 or by a pump control with the features of claim 15.

According to the invention, it is initially proposed to first wait for a stable pump operating state to detect a malfunction. A stable operating state can exist, for example, when the pump works at a constant operating point for a certain period of time. In other words, monitoring for a pump malfunction should not be active during commissioning, but should only be carried out when the desired operating point is reached. If the pump detects a stable operating state, monitoring of at least one characteristic variable of the drive motor is started in order to be able to determine, based on the monitoring of this characteristic variable, whether there is an impeller blockage. If there is an impeller blockage, the pump impeller either no longer rotates or at least turns so sluggishly that pump work can no longer be carried out sensibly.

If an impeller blockage is detected, it is proposed according to the invention to switch the pump to a freewheel in which the pump impeller can rotate freely. Ideally, this can be done by mechanically decoupling the pump shaft from the drive motor. However, it can also be provided that the motor is de-energized during freewheeling and only the braking torque of the motor is applied to the pump shaft.

If there is no impeller blockage or if one is not detected, the method instead carries out an evaluation of the frequency spectrum of the motor current, in particular at least one phase of the stator current. By evaluating the frequency spectrum, a possible impairment of the pump operation, in particular of the pump impeller, can be identified, since certain impairments, such as impending bearing damage or impeller blockage or impeller contamination due to deposits of solids on the impeller, can lead to imbalances, the oscillating harmonics of the Motor current or an amplification of these harmonics, which can be reliably identified using spectral analysis, also known as spectral analysis.

If an impairment of the pump is detected through the spectral analysis of the motor current, in particular at least one phase of the stator current, the motor is reduced to a motor speed of 0 and deactivated by running down a defined speed ramp. This means that the drive is not switched off abruptly and an immediate braking of the pump impeller, but instead a gentle speed reduction is carried out until the pump comes to a complete standstill.

The method according to the invention is preferably carried out on the integral microprocessor unit of the pump, in particular during the regular running time of the pump. However, execution on an external computing unit is also conceivable and should be included in the invention. The pump is preferably a centrifugal pump, in particular a pump for conveying media containing solids.

The detection of a stable operating state can take place, for example, by observing at least one characteristic operating parameter of the pump or the drive motor. Monitoring an electrical variable of the drive motor, in particular the motor current drawn, proves to be particularly advantageous. If the observed, characteristic parameter remains constant or approximately constant over a definable period of time or is only subject to tolerable fluctuations, the pump is assumed to be in a stable operating state and the process begins with the detection of pump impairments using spectral analysis.

It is conceivable, for example, that in the event of a detected impeller blockage and/or a pump impairment, in particular impeller contamination, a cleaning program is initiated, during which the drive motor, in particular the pump impeller, is controlled in a defined manner. Ideally, definable speed changes and reversals of rotation direction are carried out cyclically to resolve impeller blockages or impeller contamination. Ideally, individual cleaning programs can be carried out depending on the error detected. It is conceivable, for example, to carry out a first cleaning procedure if an impeller blockage is detected, and to carry out a second cleaning procedure if, on the other hand, a pump or impeller impairment is detected. In particular, the cleaning procedures are specifically tailored to the respective error case in order to achieve an optimal cleaning result.

An impeller blockage can be detected, for example, by monitoring at least one characteristic operating parameter of the pump drive, in particular the motor current drawn. A blockage is assumed, for example, if the observed characteristic size exceeds a corresponding limit or lies outside a definable interval. Ideally, an impeller blockage is assumed when the motor current drawn is greater than the rated current of the drive unit by a certain value, in particular is greater by a multiple of the rated current, for example is more than twice the rated current.

For spectral analysis, it may be sufficient to determine and monitor the spectral amplitude at at least one definable, characteristic frequency. The spectral amplitude is also referred to below as the harmonic amplitude. For example, it is conceivable that certain pump impairments lead to harmonics with certain frequencies, which are referred to below as error frequencies.

According to an advantageous embodiment of the method, the at least one definable error frequency is calculated as a function of the stator frequency of the drive motor and/or the number of pole pairs of the stator and/or as a function of the motor slip. The corresponding error frequency is particularly characteristic of possible contamination of the pump impeller.

wobei p die Anzahl an Polpaaren des Stators darstellt und f_s die Statorfrequenz ist. Bei Asynchronmotoren, insbesondere Induktionsmaschinen, ist zusätzlich der Schlupf s des Antriebsmotors zu berücksichtigen und die Formel lautet bevorzugt wie folgt: $${ƒ}_{r,pump}=\left(1\pm \frac{1}{p}\left(1-s\right)\right)\cdot {ƒ}_S$$

If the drive motor is a synchronous machine, there is no slip and the calculation formula for the error frequency f _r,pump can be defined as follows: $${ƒ}_{r,pump}=\left(1\pm \frac{1}{p}\right)\cdot {ƒ}_S,$$

where p represents the number of pole pairs of the stator and f _s is the stator frequency. For asynchronous motors, especially induction machines, the slip s of the drive motor must also be taken into account and the formula is preferably as follows: $${ƒ}_{r,pump}=\left(1\pm \frac{1}{p}\left(1-s\right)\right)\cdot {ƒ}_S$$

For the spectral analysis, the motor current/stator current measured over a period of time can be transformed into its frequency spectrum using Fast Fourier Transformation (FFT) or Discrete Fourier Transformation (DFT) in order to obtain the spectral amplitude at at least one error frequency. The spectral analysis is preferably carried out for at least one phase of the motor current in the steady state.

Since carrying out an FFT or DFT is very resource-intensive, the spectral amplitude of the motor current for at least one error frequency can alternatively also be determined using coordinate transformation. For this purpose, the transformation of the multi-phase, especially three-phase motor is used current into a two-axis dq current coordinate system. The resulting current coordinate system rotates with the error frequency of the error-indicating harmonic or the corresponding angular velocity. The resulting current vector in the dq coordinate system is therefore composed of a rotating current vector and a stationary current vector. The latter corresponds to the proportion of the motor current attributable to the harmonic, which is constant over time in the selected representation and thus forms a constant proportion of the currents i _d and i _q . In the coordinate representation, the amplitude of the error-indicating harmonic can be determined by calculating the geometric sum of these direct components. The proposed approach requires significantly fewer operations and resources than, for example, executing an FFT or DFT and can therefore be easily implemented on an internal microprocessor unit of a pump due to the comparatively low resource requirements. The solution can be implemented completely software-based on an existing microprocessor unit for controlling a centrifugal pump. Existing sensors for measuring motor currents can be used; additional hardware expansion is not required.

definiert sein kann, wobei T vorzugsweise der Abtastrate der Prozessoreinheit entspricht. Die Grenzfrequenz ω_c muss relativ klein gewählt werden, um die Schwingung so weit wie möglich zu entfernen.As already explained above, the direct components of the currents i _d and i _q , which are determined by means of transformation, provide the necessary information for determining the harmonic amplitude. A simple procedure for determining these direct current components is to use a low-pass filter, whereby the time-varying alternating component of the corresponding currents i _d , i _q is filtered out. Ideally a first order low pass filter is used. A first-order Butterworth filter is particularly preferably used in accordance with its transfer function $$H\left(\mathrm{e.g}\right)=\frac{1-e^{{\omega }_{c}T}}{\mathrm{e.g}-e^{{\omega }_{c}T}}$$

can be defined, where T preferably corresponds to the sampling rate of the processor unit. The cutoff frequency ω _c must be chosen to be relatively small in order to remove the oscillation as much as possible.

wobei ${\overrightarrow{\underset{\_}{l}}}_{\alpha \beta }$

eine Raumzeigerdarstellung des dreiphasigen Motorstroms in einem Statorkoordinatensystem und ω_F die der fehlerindizierenden Schwingungsfrequenz entsprechende Winkelgeschwindigkeit gemäß ω_F = 2πf_r,pump ist. Erforderliche trigonometrische Funktionen für die Anwendung der Park-Transformation können innerhalb der Mikroprozessoreinheit durch Look-Up-Tabellen mit einer definierten Anzahl an Wertepaaren realisiert sein, um den Speicherbedarf der Mikroprozessoreinheit zu minimieren. Denkbar ist die Verwendung von 300 bis 400 Wertepaaren, insbesondere 360 Wertepaaren.According to an advantageous embodiment of the invention, the parking transformation is used to transform the motor currents into the dq current coordinate system, in particular according to the formula $${\overrightarrow{\underset{\_}{l}}}_{dq}={\widehat{l}}_{\alpha \beta }\cdot e^{-i\left({\omega }_{F}t\right)},$$

where ${\overrightarrow{\underset{\_}{l}}}_{\alpha \beta }$

is a space vector representation of the three-phase motor current in a stator coordinate system and ω _F is the angular velocity corresponding to the error-indicating oscillation frequency according to ω _F = 2πf _r,pump . Required trigonometric functions for the application of the Park transformation can be implemented within the microprocessor unit by look-up tables with a defined number of value pairs in order to minimize the memory requirements of the microprocessor unit. It is conceivable to use 300 to 400 value pairs, in particular 360 value pairs.

The aforementioned parking transformation is often also used in a field-oriented (FOC) speed control of an electric motor, where the determination of the i _q current coordinate system does not take place depending on a specific frequency of a harmonic, but instead depending on the current rotor speed, so that in view of the rotor results in a stationary coordinate system. If this is the case, the method according to the invention can already rely on an existing control module for the implementation of a FOC to carry out the parking transformation.

Since the parking transformation requires a space vector representation of the three-phase motor current, the three-phase motor current must first be converted into a two-dimensional space vector representation. This can be done by transforming into a stator coordinate system using the Clarke transformation. Here, too, an existing control module of a FOC can theoretically be reused or instead only the information about the space vector representation is taken from the control module.

According to an advantageous embodiment, the method is carried out in particular for a wastewater pump, since impeller contamination and associated impairments to the pump often occur, especially when pumping fluids containing solids. The method according to the invention enables the wastewater pumps, which are often operated independently, to detect any undesirable impairment of their pump efficiency at an early stage and to take suitable measures to automatically eliminate corresponding impeller impairments. It is also possible to detect and differentiate a complete impeller blockage from impeller contamination.

The present invention relates not only to a method, but also to a pump train a centrifugal pump, which is designed in particular for operation as a wastewater pump. The pump according to the invention has a pump controller which is configured to carry out the method according to the present invention. Accordingly, the pump has the same advantages and properties as have already been demonstrated above using the method according to the invention. For this reason, a repeated description is omitted.

The invention also relates to a pump control for use in or with a pump, in particular a centrifugal pump, particularly preferably with a wastewater pump, the control being configured to carry out the method according to the present invention. Such a pump control can, for example, be an integral part of a pump, but can also be designed as an external module that is only communicatively connected to a corresponding pump unit in order to carry out the method according to the invention. It is also conceivable that such a pump control is connected to more than one pump unit and monitoring, in particular parallel monitoring, of several pump units is possible.

• 1: ein Ablaufdiagramm einer ersten Ausgestaltung des erfindungsgemäßen Verfahrens,
• 2: eine Diagrammdarstellung des Spektrums einer Phase des aufgenommenen Motorstroms,
• 3: ein zweites Ablaufdiagramm zur Verdeutlichung einer zweiten Ausgestaltung des erfindungsgemäßen Verfahrens,
• 4: eine Gegenüberstellung des stationären Stator-Koordinatensystems sowie des rotierenden d-q-Koordinatensystems,
• 5: eine Darstellung des mit der Fehlerfrequenz rotierenden d-q-Koordinatensystems für die Fehleranalyse und
• 6: eine Blockdarstellung zur Verdeutlichung der einzelnen Verfahrensschritte zur Fehlerüberwachung

Further advantages and properties of the invention will be explained below using the exemplary embodiments shown in the figures. Show it:

• 1 : a flowchart of a first embodiment of the method according to the invention,
• 2 : a diagram representation of the spectrum of a phase of the motor current drawn,
• 3 : a second flow chart to illustrate a second embodiment of the method according to the invention,
• 4 : a comparison of the stationary stator coordinate system and the rotating dq coordinate system,
• 5 : a representation of the dq coordinate system rotating with the error frequency for error analysis and
• 6 : a block diagram to illustrate the individual process steps for error monitoring

1 shows the flowchart of a first embodiment of the method according to the invention for monitoring the operation of a wastewater pump. The pump has at least one impeller that is driven by a multi-phase electric motor.

When the pump is started up, the pump is first ramped up to the desired operating speed according to a defined speed ramp (block 100). After reaching the operating speed, the pump switches to regular pump operation (block 200). During regular pump operation, a check is made to see whether the pump is in a stable operating state (block 300). For this purpose, the motor current drawn by the motor is recorded. If the motor current remains constant or almost constant for a certain period of time, the existence of a stable operating point is assumed and the method goes to step 400.

In block 400, the recorded motor current of at least one phase of the drive motor is compared against a limit value, which here corresponds to twice the rated motor current 2*I _nominal . If the motor current drawn exceeds this limit value, it is concluded that the pump impeller is blocked and the pump control initiates an immediate pump stop. For this purpose, the motor is immediately switched off and the pump impeller is forced to freewheel (block 500), which reduces the risk of damage to the impeller due to the detected blockage. The method then moves to block 600 to start a pump cleaning process specifically tailored to an impeller blockage. The cleaning process may include a sequence of changes in the direction of rotation of the impeller to force the blockage to clear. If the cleaning process was successful, the process returns to the starting point for starting up the pump (block 100).

However, if the detected motor current in block 400 remains below the limit value 2*I _nominal , ie there is no impeller blockage, a spectral analysis of the motor current of at least one phase is carried out instead (block 700). This is done, for example, by high-frequency and highly sampled current measurement and second-by-second evaluation of the frequency band of the current signal. Based on this, the spectral amplitude iF is calculated and monitored at the error frequency f _r,pump . In the execution of the 1 The spectral amplitude is calculated by transforming the time course of the detected motor current into its frequency spectrum, either using Discrete Fourier Transformation (DFT) or Fast Fourier Transformation (FFT).

In 2 For example, the frequency spectrum of one phase of the recorded stator current is shown, namely “free” for the error-free case and “clogged” for the case of impeller contamination. The two marked circles 80 indicate the amplitudes of the sidebands of the Current spectrum that is characteristic of certain impairments in the pump function and is therefore referred to as error or damage frequencies. Oscillating harmonics of the motor current with these frequencies should be seen as an indication of the existence of an impairment, for example an imbalance or an alignment error of the mechanics in the hydraulic and drive part of the pump. This imbalance and alignment error can be caused by a clogged impeller, a bearing error or the pump running dry. In this case, it can be clearly seen that the spectral amplitudes at the identified damaging frequencies 80 increase significantly if the impeller of the pump has significant buildup.

The relevant error frequency f _r,pump mentioned can be calculated using an error model that calculates the error frequency according to formula (1) as a function of the stator frequency (rotor speed n), the motor slip s and the number p of pole pairs of the drive motor: $${ƒ}_{r,pump}=\left(1\pm \frac{1}{p}\left(1-s\right)\right)\cdot {ƒ}_s.$$

Clearly, the slip s can only be used when using an asynchronous machine as the drive motor. If a synchronous machine is used as the drive motor instead, a slip s = 0 can be used in the above formula.

The spectral amplitude iF determined for the at least one characteristic error frequency f _r,pump is compared in block 800 against a limit value iF,Lim. If the limit value is exceeded, the method concludes that the pump impeller is impaired, in particular impeller contamination that impairs efficiency, and in response initiates a shutdown of the drive unit. However, the second requirement here is that the limit value has been exceeded for at least 3 seconds (block 900).

In contrast to the case of an impeller blockage, when impeller contamination is detected, the drive motor is not immediately switched off, but instead the pump is braked moderately by running down a speed ramp to speed 0 (block 1000) until the impeller comes to a standstill. Only then is a second cleaning procedure (block 1100) carried out, which deviates from the first cleaning procedure 600.

The 3-6 show a modified embodiment of the method according to the invention. The block diagrams of the 2 and 3 agree except for blocks 700, 800, 700', 800', ie the spectral analysis of the motor current, so that identical reference numbers are used in both figures for identical process steps and only the difference in blocks 700', 800' will be discussed below becomes. The 4 , 5 show a diagram to illustrate the procedure. 6 shows a block diagram that describes the process in block 700 in more detail.

For error monitoring at the specific frequencies of the current spectrum, the principle of multiple reference frame theory is used instead of using FFT or DFT in order to minimize the memory effort and the number of operations. The idea is, similar to field-oriented control (FOC), to rotate a coordinate system. While in FOC the coordinate system rotates at the frequency of the rotor, in the sense of error detection it rotates at the frequency of an error. As already explained above, at least one error frequency is determined using the formula given under (1). This is in the diagram 6 identified by the reference number 10.

In a three-phase motor, the motor currents can be combined in a spatial vector. It is assumed that the sum of the phase currents is zero. The real part of the space vector is called α-current and the imaginary part is called β-current. The α-β coordinate system (see 4 ) is called the stator-fixed coordinate system (stator coordinate system). The transformation from the three-phase stator currents to the two-phase α-β current is called the Clarke transformation.

In order to drive an AC motor, the stator-fixed α-β current is transformed by the controller into the rotor-fixed d-q current, which is referred to as the park transformation. Mathematically speaking, a coordinate system is made to rotate according to the speed n of the rotor. As a result, the d-q current is a DC value that can be used for motor control. The interesting aspect is that the vector sum of d and q current corresponds exactly to the amplitude of the fundamental wave of the motor current. The modified version of the method makes use of this principle for error detection.

If you look at a real motor, the phase current and thus the current space vector is superimposed with oscillations, the extent of which increases if the pump or drive motor is operating incorrectly. For the method according to the invention it is now assumed that the motor current The sum of the torque-forming current with the amplitude î _T and the speed ω _S and a harmonic with the amplitude î _F and the speed ω _F is. The motor currents of the three phases can be calculated using the following equations (2): $$\begin{array}{l}{i}_a\left(t\right)={\widehat{l}}_T\text{cos}\left({\omega }_{S}t\right)+{\widehat{l}}_F\text{cos}\left({\omega }_{F}t+\theta \right)\\ i_b\left(t\right)={\widehat{l}}_T\text{cos}\left({\omega }_{S}t-\frac{2\pi }{3}\right)+{\widehat{l}}_F\text{cos}\left({\omega }_{F}t+\theta -\frac{2\pi }{3}\right)\\ i_c\left(t\right)={\widehat{l}}_T\text{cos}\left({\omega }_{S}t-\frac{4\pi }{3}\right)+{\widehat{l}}_F\text{cos}\left({\omega }_{F}t+\theta -\frac{4\pi }{3}\right)\end{array}$$

In this case, î _F contains information about the status of the pump and the severity of the error. As an example, ω _F can be calculated based on equation (1).

im Stator-Koordinatensystem gleich der Summe aus der drehmomentbildenden Komponente ${\overrightarrow{\underset{\_}{l}}}_{T|\alpha \beta },$

die mit der Drehzahl ω_S rotiert, und der Fehlerkomponente ${\overrightarrow{\underset{\_}{l}}}_{F|\alpha \beta },$

die mit der Drehzahl ω_F rotiert. Die Berechnung des Stromraumvektors ${\overrightarrow{\underset{\_}{l}}}_{\alpha \beta }$

des dreiphasigen Motorstroms erfolgt gemäß der nachfolgenden Gleichung (3): $${\overrightarrow{\underset{\_}{l}}}_{\alpha \beta }={\widehat{l}}_T\cdot e^{i\left({\omega }_{S}t\right)}+{\widehat{l}}_F\cdot e^{i\left({\omega }_{F}t+\theta \right)}$$

As in 4 shown is the current space vector ${\overrightarrow{\underset{\_}{l}}}_{\alpha \beta }$

in the stator coordinate system equal to the sum of the torque-generating component ${\overrightarrow{\underset{\_}{l}}}_{T|\alpha \beta },$

which rotates with the speed ω _S , and the error component ${\overrightarrow{\underset{\_}{l}}}_{F|\alpha \beta },$

which rotates at speed ω _F. The calculation of the current space vector ${\overrightarrow{\underset{\_}{l}}}_{\alpha \beta }$

of the three-phase motor current occurs according to the following equation (3): $${\overrightarrow{\underset{\_}{l}}}_{\alpha \beta }={\widehat{l}}_T\cdot e^{i\left({\omega }_{S}t\right)}+{\widehat{l}}_F\cdot e^{i\left({\omega }_{F}t+\theta \right)}$$

In the block diagram shown the 6 This step is already carried out by the existing field-oriented control 20 of the pump control, which supplies the two currents i _a and i _β as output variables.

von Interesse. Nun wird das d-q-Koordinatensystem mit der Geschwindigkeit der Oberschwingungsfrequenz (ω_K = ω_F) gedreht. Zur Berechnung des Stromvektors in d-q-Koordinaten wird die Standardgleichung für die Park-Transformation verwendet, was im Blockdiagramm durch den Schritt 30 gekennzeichnet ist. Die Park-Transformation lässt sich mathematisch gemäß folgender Gleichung umsetzen: $${\overrightarrow{\underset{\_}{l}}}_{dq}={\overrightarrow{\underset{\_}{l}}}_{\alpha \beta }\cdot e^{-i\left({\omega }_{F}t\right)}$$

In the sense of the method according to the invention, the length is: ${\overrightarrow{\underset{\_}{l}}}_{F|\alpha \beta }$

of interest. Now the dq coordinate system is rotated at the speed of the harmonic frequency (ω _K = ω _F ). To calculate the current vector in dq coordinates, the standard Park transform equation is used, which is indicated by step 30 in the block diagram. The Park transformation can be implemented mathematically according to the following equation: $${\overrightarrow{\underset{\_}{l}}}_{dq}={\overrightarrow{\underset{\_}{l}}}_{\alpha \beta }\cdot e^{-i\left({\omega }_{F}t\right)}$$

im d-q-Koordinatensystem: $${\overrightarrow{\underset{\_}{l}}}_{dq}={\widehat{l}}_F\cdot e^{i\theta }+{\widehat{l}}_T\cdot e^{i\left[\left({\omega }_S-{\omega }_F\right)t\right]}$$

Substituting formula (3) into formula (4) results in formula (5) for the current vector ${\overrightarrow{\underset{\_}{l}}}_{dG}$

in the dq coordinate system: $${\overrightarrow{\underset{\_}{l}}}_{dq}={\widehat{l}}_F\cdot e^{i\theta }+{\widehat{l}}_T\cdot e^{i\left[\left({\omega }_S-{\omega }_F\right)t\right]}$$

ist gleich der Summe der Vektoren ${\overrightarrow{\underset{\_}{l}}}_{T|dq},$

die mit der Geschwindigkeit (ω_S - ω_F) rotieren, und dem stationären Vektor ${\overrightarrow{\underset{\_}{l}}}_{F|dq},$

siehe 5. enn ω_F größer als ω_s ist, drehen sich sowohl ${\overrightarrow{\underset{\_}{l}}}_{dq}$

als auch ${\overrightarrow{\underset{\_}{l}}}_{T|dq}$

in die andere Richtung.The three-phase vector ${\overrightarrow{\underset{\_}{l}}}_{dq}$

is equal to the sum of the vectors ${\overrightarrow{\underset{\_}{l}}}_{T|dq},$

which rotate with the speed (ω _S - ω _F ), and the stationary vector ${\overrightarrow{\underset{\_}{l}}}_{F|dq},$

please refer 5 . If ω _F is greater than ω _s , both rotate ${\overrightarrow{\underset{\_}{l}}}_{dq}$

as well as ${\overrightarrow{\underset{\_}{l}}}_{T|dq}$

in the other direction.

$$i_q=i_{F|q}+i_{T|q}\cdot \text{sin}\left(\left({\omega }_S-{\omega }_F\right)t\right)$$

Considering time-dependent quantities, i _d and i _q consist of a DC component and an AC component, as can be seen in equations (6) and (7). $$i_d=i_{F|d}+i_{T|d}\cdot \text{cos}\left(\left({\omega }_S-{\omega }_F\right)t\right)$$

$$i_q=i_{F|q}+i_{T|q}\cdot \text{sin}\left(\left({\omega }_S-{\omega }_F\right)t\right)$$

The initial amplitude î _f can be calculated from the geometric sum of i _Fld and i _Flq , see equation (8) below. $${\widehat{l}}_{ƒ}=\sqrt{i_{F|\mathrm{<figure-callout\; id="2"\; label="d"\; filenames="DE102022106063A1\_0032.png,DE102022106063A1\_0033.png"\; state="\{\{state\}\}">d</figure-callout>}}{}^2+i_{F|\mathrm{<figure-callout\; id="2"\; label="q"\; filenames="DE102022106063A1\_0032.png,DE102022106063A1\_0033.png"\; state="\{\{state\}\}">q</figure-callout>}}{}^2}$$

In the block diagram of the 6 This process step is marked with the reference number 50. If the direct current components of i _d and i _q are determined, the amplitude î _f can be calculated from this. The amplitude of a harmonic can be calculated by using simple transformations. A simple and memory friendly method to calculate the DC components of i _d and i _q is a first order filter shown in the block diagram of the 6 is marked with the reference number 40.

wobei T gleich der Abtastzeit der Mikroprozessoreinheit ist. Das Filter erlaubt eine einfache Implementierung. Allerdings muss die Grenzfrequenz ω_c relativ klein gewählt werden, um die Schwingung so weit wie möglich zu entfernen. Dadurch wird die Zeitkonstante des Filters relativ hoch, was das System langsam macht und in dynamischen Systemen ein Problem darstellen kann. Beim Einsatz in einer Pumpe ist dies jedoch unkritisch, da keine schnellen Lastwechsel zu erwarten sind.For example, a first-order Butterworth filter can be chosen, the transfer function of which can be determined as follows according to equation (9). $$H\left(\mathrm{e.g}\right)=\frac{1-e^{{\omega }_{c}T}}{\mathrm{e.g}-e^{{\omega }_{c}T}},$$

where T is equal to the sampling time of the microprocessor unit. The filter allows for easy implementation. However, the cutoff frequency ω _c must be chosen to be relatively small in order to remove the oscillation as much as possible. This makes the time constant of the filter relatively high, which makes the system slow and can be a problem in dynamic systems. However, this is not critical when used in a pump, as no rapid load changes are to be expected.

The value for the spectral amplitude î _f determined as described above could then be in block 800` as an alternative to the representation in 3 compared against a limit value iF,Lim, whereby if it is exceeded for a period of at least 3s (Block 900) also causes the pump to stop (Block 1000) and then the cleaning procedure (Block 1100) is triggered.

However, as an alternative to this variant, as in 3 shown, in block 700` not only the spectral amplitude î _f , as described above, is determined, but also the damage factor SF instead. Particularly with controlled pumps, for example pressure-controlled pumps, the load and speed of the pump can change during operation, which also means a change in the power consumption of the pump. To take this into account, the damage factor (“Severity Factor” SF) is calculated for an error that relates to the current consumption. This is shown in the block diagram 6 with the reference number 60. If the motor control of the pump has a FOC 20, the information about the current consumption is available. In order to ensure load independence, the damage factor SF is formed from the ratio of the error-indicating spectral amplitude î _f and the amplitude î _T of the torque-forming component, which is equal to the q-current in the FOC used, with the d-current being controlled to zero : $$SF=\frac{{\widehat{l}}_{ƒ}}{{\widehat{l}}_T}\cdot 100\%.$$

Based on the damage factor SF, a decision can then be made in block 800 (see 3 and 6 ) by comparing it with a limit value SF, Lim, it can be determined whether the pump has impeller contamination or not. If this is detected, for a period of more than 3 seconds, the pump is reduced to a speed of zero (block 1000) and then cleaning procedure 2 is started (block 1100).

Claims (15)

Method for monitoring the operation of a pump, preferably a centrifugal pump (1), with a multi-phase, in particular three-phase drive motor, with the method steps: - Determine whether the pump is operating in a stable operating state, - If there is a stable operating state, monitoring at least one characteristic variable of the drive motor to determine whether there is an impeller blockage, - if an impeller blockage is detected, activate a freewheel of the pump impeller, - Otherwise, evaluation of the frequency spectrum of the motor current to detect impairment of the pump and switching off the motor by running down a decreasing speed ramp if impairment of the pump is detected. Procedure according to Claim 1 , characterized in that an impairment of the pump is an impairment of the pump impeller, in particular impeller contamination. Procedure according to Claim 1 or 2 , characterized in that a cleaning program is initiated when an impeller blockage and/or an impeller blockage is detected. Procedure according to Claim 3 , characterized in that after an impeller blockage is detected, a first cleaning program is carried out and after an impeller blockage is detected, a second cleaning program is carried out. Method according to one of the preceding claims, characterized in that an impeller blockage occurs by monitoring the recorded motor current, a blockage being detected when the motor current exceeds a definable limit value, in particular exceeds the rated current by a certain value, preferably over a multiple of the rated current lies. Method according to one of the preceding claims, characterized in that the evaluation of the frequency spectrum includes monitoring a spectral amplitude of the motor current at at least one definable error frequency. Procedure according to Claim 6 , characterized in that the at least one error frequency is determined depending on the pole pairs of the stator and / or the stator frequency and / or a possible motor slip, in particular according to ${ƒ}_{r,pump}=\left(1\pm \frac{1}{p}\left(1-s\right)\right)\cdot {ƒ}_s$

for an induction motor and for a synchronous motor ${ƒ}_{r,pump}=\left(1\pm \frac{1}{p}\right)\cdot {ƒ}_s,$

where p is the number of pole pairs of the stator, s is the motor slip and f _{s is} the stator frequency. Procedure according to Claim 6 or 7 , characterized in that the spectral amplitude is determined using Fast Fourier Transformation or Discrete Fourier Transformation. Method according to one of the above Claims 6 or 7 , characterized in that the spectral amplitude î _f of the motor current for the at least one specific error frequency f _r,pump by transforming the three-phase motor current into one with the error frequency f _r,pump rotating d/q current coordinate system with the currents i _d and i _q is calculated, whereby the geometric sum of the direct components of the currents i _d and i _q in the d/q current coordinate system corresponds to the spectral amplitude î _f . Method according to one of the preceding claims, characterized in that the direct components of the transformed currents i _d and i _q are determined by using a low-pass filter, preferably a first-order low-pass filter, particularly preferably a first-order Butterworth filter. Procedure according to Claim 9 or 10 , characterized in that the transformation into the dq current coordinate system takes place by means of Park transformation, in particular according to $${\overrightarrow{\underset{\_}{l}}}_{dq}={\overrightarrow{\underset{\_}{l}}}_{\alpha \beta }\cdot e^{-i\left({\omega }_{F}t\right)},$$

where ${\overrightarrow{\underset{\_}{l}}}_{dq}$

is a space vector representation of the three-phase motor current in a stator coordinate system and the angular velocity ω _F is calculated from the error frequency f _r,pump according to ω _F = 2πf _r,pump . Procedure according to Claim 11 , characterized in that the transformation of the three-phase motor current into the space vector representation in the stator coordinate system is carried out by a Clark transformation, whereby the space vector ${\overrightarrow{\underset{\_}{l}}}_{\alpha \beta }$

is preferably determined by an existing control module of the pump control, which carries out a field-oriented speed control (20). Method according to one of the preceding claims, characterized in that the pump is a wastewater pump. Pump, preferably centrifugal pump, in particular for operation as a wastewater pump, with a pump control which is configured to carry out the method according to one of the preceding claims. Pump control for a pump, in particular a centrifugal pump, configured to carry out the method according to one of the above Claims 1 until 13 .

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